The present invention relates to idler or transfer rolls of the type used in, for example, annealing ovens and more particularly to such rolls that, because of their structure allow for reduced thermal fatigue and consequently extended roll life over those of the prior art.
The provision of transfer or idler rolls for the transport of material, for example, steel through annealing ovens and the like has been the subject of development for a number of years. At one point such rolls comprised steel that extracted heat at an unacceptable rate. Subsequently, rolls that utilized compacted particulate inorganic materials as a back-up to a steel surface sleeve were designed and used. While these rolls provided some improvement over the steel variety, the compacted inorganic material proved to be too xe2x80x9csoftxe2x80x9d and over time resulted in the surface of the roll sagging in the area filled with the inorganic material thus resulting in failure of the roll.
In 1999, Hart et al in U.S. Pat. No. 5,989,170 described a roll structure that comprised a plurality of annular discs of a highly compacted ceramic fiber about a central cooling water conduit. Again, while this structure provided an apparent improvement in roll capability by limiting the amount of heat extracted by the roll and providing extended roll life, it was not entirely satisfactory for a number of reasons that are pointed out in U.S. Pat. No. 6,196,957 to Hiraguri et al issued Mar. 6, 2001.
Hiraguri et al describe an insulating roll that is constructed with a roll body formed of a plurality of inorganic material derived discs laminated with each other and positioned axially of and around a metal conduit, and a heat resistant metal tube or shell disposed integrally over an outer periphery of the roll body. The roll described in Haraguri et al is claimed to have low thermal conductivity, and high impact strength without involving reduction of the surface temperature of a material being heat treated in a furnace or reducing the ambient temperature in the furnace during heat treatment. It is to be noted that the claims of this patent were ultimately limited to a structure for retaining the tubular shell on the roll structure. Again, while this revised structure apparently provided some benefits as claimed, the roll demonstrated an inability to operate at very high temperatures, above about 2000xc2x0 F., due to the presence of welds used to attach a variety of the members to a hollow core. It is also to be specifically noted that in the roll of Hiraguri et al, the axially oriented inorganic material discs are in direct contact with the overlying steel shell at their outer peripheries.
Subsequent to the development described in Hiraguri et al, various apparently unpatented attempts were made to alter the heat transfer characteristics of Hiraguri et al""s roll. Among these were the insertion of so-called xe2x80x9cfoilsxe2x80x9d, i.e. thin strips of stainless steel located between adjacent inorganic material discs or sets of discs that extended partially through the thickness dimension of the array of discs from the outer periphery of the interior water cooling channel outward toward the steel shell. The presence of such xe2x80x9cfoilsxe2x80x9d apparently increase the heat exchange capability of the roll of Hiraguri et al a small amount. Again, while this appears to have provided a step in the right direction, it was not enough to adequately extend roll surface shell life.
Accordingly, there remains the need for improvement in the structure of these so-called xe2x80x9cinsulating rollsxe2x80x9d to extend the useful operating life of the steel shell while minimizing heat extraction from the heat treatment process.
It is therefore an object of the present invention to provide a roll structure that provides minimal heat extraction from the heat treatment process while providing sufficient heat extraction from the roll surface to optimize the life of the operating life of the roll surface shell.
It is another object of the present invention to provide a novel method for the attachment of a tubular shell to a water cooled roll.
According to the present invention, there is provided, an insulating roll comprising: a metal conduit having an outer peripheral portion; a plurality of discs having outer peripheries and fabricated from an inorganic material positioned axially on and around the metal conduit; a tubular shell having an inner surface about and spaced apart from said outer peripheries; metallic foils extending between each or a plurality of said discs from said outer peripheral portion to and beyond said outer peripheries to the inner surface of the tubular shell, said metallic foils being in interference or frictional contact with said inner surface. A novel method for attaching the tubular shell to the conduit to simplify removal and replacement thereof is also described.